1. Field of the Invention
An invention relates to a vacuum arc vapor deposition method and apparatus for forming a thin film over a surface of a substrate in order to improve a weary resistance property of such a substrata as an automobile part, machine part, machine tool, and metal mold, and more particularly relates to the generation and control of a magnetic field by a magnetic filter.
2. Description of The Related Art
Generally, a vacuum arc deposition is a simple thin film forming process in which arc discharge is caused between a cathode and an anode, and cathode material evaporates to deposit on a substrate to form a thin film thereon. A process is excellent in film production efficiency.
In the vacuum arc deposition process, however, large particles (droplets) of several μm in diameter are emitted from a cathode material (also from the cathode in some discharging conditions). Then, the droplets deposit to the substrate to thereby deteriorate characteristics of forming the film, as known.
To prevent the droplets from deteriorates the characteristics of forming film, some vapor depositing techniques are proposed. A first vapor depositing technique removes the droplets by a magnetic field, which is developed between the cathode and the substrate by use of the magnets, e.g., electromagnetic coils, whereby only a plasma stream is transported along the magnetic field to the substrate. Another technique focuses the plasma to increase a density of the plasma by use of such a magnetic field, and melts the droplets by the high density plasma.
A vacuum arc vapor deposition method and apparatus for removing the droplets and transporting only the plasma stream to the substrate is disclosed by, for example, JP-A-2001-59165 (C23C14/32), Which is filed by the applicant of the present patent application.
The vacuum arc vapor deposition apparatus (arc type ion plating apparatus) as disclosed is constructed as shown in a plan view of FIG. 9.
A metallic vacuum vessel 2, which forms a film forming chamber 1 is evacuated through an exhaust port 3 by a vacuum discharging device (not shown). An inactive gas such as an argon gas or a reaction gas is introduced into the metallic vacuum vessel 2 through a gas introducing port 4 on the left side.
In JP-A-2001-59165, a structure is illustrated in which a plurality of substrates is attached to a cylindrical holder in the film forming chamber 1. In FIG. 9, for simplicity of explanation, one plate-like holder 5 Is placed at a central part in the film forming chamber 1. The holder 5 is rotatably provided while its surface is forwardly directed to a metallic duct 9. A substrate 6 is detachably held on the surface of the holder 5.
The substrate 6 is connected to the cathode of a bias power source 7, through the holder 5, and is DC pulse biased to typically −0.5 kV to 5.0 kV with respect to the vacuum vessel 2.
In FIG. 9, reference numeral 8 designates an insulating member which is provided on a rear surface of the vacuum vessel 2 and for insulating the cathode of a bias power source 7.
The metallic duct 9, rectangular in cross section, is extended forward from the metallic vacuum vessel 2, while being curved to the left (in the FIG. 9). An evaporating source 11 is provided at the central part of an end plate 9′. One end of the end plate 9′ is earthed. The evaporating source 11 is located at the front end of the duct 9 in a state that an insulating member 10 is interposed between them. A cathode of an arc power source 12 of about several tens V is connected to the evaporating source 11. An anode of the arc power source 12 is earthed. Therefore, the duct 9 works as an anode and the evaporating source 11 works as a cathode.
An anode electrode is severally provided instead of the duct 9.
The evaporating source 11 includes a water-cooling mechanism, vacuum sealing mechanism, trigger mechanism and the like.
Magnetic field generating coils 14a to 14d, while surrounding the duct 9, are provided at a plurality of positions between both ends of the duct 9.
The magnetic field generating coils 14a to 14d, numbered #1 to #4 from on a end of the duct 9, are disposed parallel to the cross section of the duct 9.
The electromagnetic coil 14d of the terminal magnet is disposed parallel to the cross section of the duct 9 and the plasma injection plane of a plasma injection hole 13 and the substrate.
The magnetic field generating coils 14a to 14d are connected in series between the output terminals of a coil power source 15 as a current source. Coil current or the magnetic field generating coils 14a to 14d is controlled under coil current control of the control unit 16. When the controlled current is fed to the magnetic field generating coils 14a to 14d, a deflection magnetic field 17a is generated which is curved along the duct 9 as indicated by a solid line loop. The deflection magnetic field 17a forms a magnetic filter 18a. 
Magnetic field generating coils 14a to 14d are provided at a plurality of positions between both ends of the duct 9, while surrounding the duct 9. Those magnetic field generating coils 14a to 14d are numbered #1 to #4 from one end of the duct 9.
The #4 electromagnetic coil 14d as the terminal magnet closest to the plasma injection hole 13, and the remaining #1 to #3 electromagnetic coils 14a to 14c are equal in the number of turns and in size.
The electromagnetic coil 14d is substantially parallel to the cross sectional plane of the duct 9, which is perpendicular to the extending direction of the duct 9 as indicated by a two-dot chain line, and parallel to the plasma injection surface of the plasma injection hole 13. The remaining electromagnetic coils 14 are also substantially parallel to the cross sectional plane of the duct 9.
The other end of the duct 9 is mounted oh the central part of the front plate 2″ of the vacuum vessel 2. The plasma injection hole 13 of the other end of the duct 9 communicates with the film forming chamber 1. The center of the plasma injection plane of the plasma injection hole 13, which extends horizontally (to the horizontal directions), is aligned with the center of the combination of the holder 5 and substrate 6.
In the vacuum arc vapor deposition apparatus, vacuum arc discharge occurs between the duct 9 as the anode and the evaporating source 11 as the cathode. At this time, conductive, cathode materials 19, such simple metals of the evaporating source 11 as Ti, Cr, Mo, Ta, W, Al and Cu, and alloys, e.g., TiAl, are evaporated from the evaporating source.
Plasma streams 20a, indicated by broken lines with arrows, containing electrons generated by the arc discharge and ions of the cathode material 19 are transported from one end of the duct 9 to the plasma injection hole 13 located at the other end thereof, along the deflection magnetic field 17a. 
Each droplet emitted from the evaporating source 11 is electrically neutral or negatively charged in the plasma. In any case, the mass of the droplet is considerably large. Accordingly, it moves straight forward independently of the deflection magnetic field 17a to impinge on the inner wall of the duct 9, so that the droplet is removed from the plasma stream 20a. Therefore, the droplet rails to reach the surfaces of the substrate 6 and the holder 5.
Ions of the cathode material 19 having arrived at the plasma injection hole 13 are led into the film forming chamber 1 under a negative bias potential of the substrate 6 caused by the bias power source 7. The ions are sputtered onto the surface of the substrate 6 to thereby form a vapor deposited film made of the cathode material 19 on the surface of the substrate 6.
A reaction gas is introduced into the film-forming chamber 1 through the gas introducing port 4. Then, the gas reacts with ions of the cathode electrode material 19 to vapor deposit on the surface of the substrate 6 a thin film of metal compound, such as titanium carbide, titanium nitride, alumina and titanium dioxide.
When the reaction gas is not introduced, a carbon film or the like is formed by vapor deposition an the surface of the substrate.
In the vacuum arc vapor-deposition by the conventional apparatus of FIG. 9, the electromagnetic coil 14d of the terminal magnet is disposed parallel to the plasma injection plane of the plasma injection hole 13 and the substrate 6.
In the vacuum arc deposition of the conventional vacuum arc vapor deposition apparatus of FIG. 9, the magnetic field generating coils 14a to 14d are disposed parallel to the cross section of the duct 9, and the generated magnetic field characteristics of the magnetic filter 18a are fixed to various characteristics as defined by their installing conditions.
In the vacuum arc vapor-deposition by the conventional apparatus of FIG. 9, the electromagnetic coil 14d of the terminal magnet is disposed parallel to the cross sectional plane of the duct 9, and the plasma injection surface of the plasma injection hole 13 and the substrate 6. The remaining electromagnetic coils 14a to 14c are also substantially parallel to the cross sectional plane or the duct 9 at their positions.
When an electron is transported in a uniform magnet field, as well known, the electron receives Lorentz forces F given the following formula 1.F=q·(v×B)  [Formula 1]where v=electron (outer) velocity in a direction perpendicular to the magnetic field    B=magnetic field    x=operator of the vector product    ·=operator of the inner vector
Under the Lorentz forces F, the electron travels along the magnetic field lines of a deflection magnetic field 17a, while spirally rotating.
Ions of the cathode material 19 travel within and along the duct 9 while being pulled by the electrons, and are transported to the plasma injection hole 13.
At this time, in the vicinity of the electromagnetic coil 14d as the terminal magnet, as indicated by magnetic field lines of solid lines in FIGS. 10A and 10B a diverging magnetic field is present. Electrons and ions having reached the plasma injection hole 13 travel along the diverging magnetic field.
FIGS. 10A and 10B are a plan view and a right side view showing a distribution of magnetic field lines developed respectively when current is fed to only the two magnetic field generating coils 14b and 14d of those magnetic field generating coils 14a to 14d, viz.
The traveling paths of electrons along the magnetic field lines correspond to the traveling paths of ions of the cathode electrode material 19, which travel while being attracted by electrons. Therefore, one can grasp the paths of ions of the cathode electrode material 19 from the electron traveling paths.
The traveling paths of electrons by the magnetic field lines of FIGS. 10A and 10B are as illustrated in a plan view and a right side view of FIGS. 11A and 11B.
Under the diverging magnetic field, a position on the substrate at which the electron arrives is horizontally deflected from the center of the substrate 6 and diverged in up and down directions (vertical directions) in accordance with its curving direction.
As shown in a plan view of FIG. 19, a centrifugal force Fcf of an outward direction, a magnetic field inclination (gradient) ∇B of an inward direction act on electrons and ions in a vacuum curved magnetic field, such as the deflection magnetic field 17a, and drifts occur as given by the following formula 2.v(R)+v(∇B)=(m/q)·(Rc×B)·(v(∥)+v(⊥)2/2)  [Formula 2]where    v(R=velocity drift of Fcf    v(∇B)=velocity drift of v(∇B)    m=mass    (v(∥)=velocity in the B direction (extending direction) of the duct 9    V(⊥)=velocity of the vertical line    Rc=radius of curvature at a position x in FIG. 19    q=electric charge
In the above equation, “Rc×B” indicates a vector having a direction in which a right-handed screw advances when the radius or curvature Rc is rotated while being placed on the magnetic field B.
Ions in the plasma 20a show a tendency that the ions travel while being drawn by electrons. By the drift effect, the ion depositing position is further deviated from a target position.
The cross section of the duct 9 and the magnetic field generating coils 14a to 14d are each rectangular in cross section. Because of the magnetic field characteristics of the magnetic field generating coils 14a to 14d, the inclination ∇B of the magnetic field increases toward the outer side of the cross section. Accordingly, the drift velocity having an obliquely downward direction increases, and hence, the divergence to a downward direction increases.
In the vacuum arc vapor deposition apparatus of this type which removes droplets by use of the magnetic filter 18a, it is difficult vapor deposit a thin film of the cathode electrode material 19 at a target position on the substrate 6 so as to have a thin film of an intended thickness. In this respect, the conventional vacuum arc vapor deposition apparatus described above is not satisfactory in obtaining a uniform film forming characteristic.
Similar problems arise independently of the number of evaporating sources 11.
A possible approach for ameliorating the film forming characteristics is present in which by adjusting installing angles (inclinations) of the magnetic field generating coils 14a to 14d, a magnetic field generated by the magnetic filter 18a is set and controlled to correct the traveling paths (plasma path) of ions and electrons. To adjust installing angles (inclinations) of the magnetic field generating coils 14a to 14d by actually moving the magnetic field generating coils 14a to 14d, a complicated and expensive 3-dimensional rotary mechanism for moving the magnetic field generating coils 14a to 14d must be used. Therefore, it is impossible to set and control the magnetic field characteristics generated by the magnetic filter 18a through an easy and inexpensive adjustment.
Let us consider a case where three evaporating sources 11 are vertically disposed and of those evaporating sources, the top evaporating source 11 named as an upper cathode, the middle one, as a middle cathode, and the bottom one, as a lower cathode. The electrons emitted mainly from the upper cathode are affected by the upward curve of the magnetic field B, and the electrons emitted from the lower cathode are affected mainly by the downward curve of the magnetic field B. The electrons from the upper and lower cathodes drift in the following directions in accordance with the forward and reverse directions (clockwise and counterclockwise) of the coil current when one sees from the cathodes to the substrate 6, as shown in Table 1. The electron drift direction is symmetrical with respect to the upper and lower cathodes and the forward and reverse directions of the coil current.
TABLE 1Drift directionCurrent directionsClockwiseCounterclockwiseCathodeUpperLower leftUpper rightLowerLower rightUpper left
Ions in the plasma 20a show a tendency that the ions travel while being drawing by electrons.
By the drift effect, an ion depositing position is further deviated from a target position.
In the vacuum arc vapor deposition apparatus of this type which removes droplets by use of the magnetic filter 18a, it is difficult vapor deposit a thin film of the negative electrode material 19 at a target position on the substrate 6 so as to have a thin film of an intended thickness. In this respect, the conventional vacuum arc vapor deposition apparatus described above is not satisfactory in obtaining a uniform film forming characteristic.
Similar problems arise independently of the number of evaporating sources 11 in the vacuum arc deposition of this type which removes the droplets by the utilization of the function of the magnetic filter.
in other case, a diverging magnetic field B has a gradient ∇B. Charged particles, e.g., electrons, drift in a direction in which a right-handed screw advances when the gradient ∇B rotates at a velocity B given by the following formula 102, while being placed on the diverging magnetic field B. The ∇B drift further deviates the electron path.VB=−μ·(∇B×B)/(q·B2)  [Formula 102]where μ=magnetic permeability    q=electric charge    B=magnetic field vector,    ∇B=gradient vector of the magnetic field B,    x=operator of the vector product    ·=operator of the inner vector
In this situation, it is impossible to land ions of the cathode material 19 at desired positions, e.g., the central part on the surface of the substrate 6, and therearound.
The cross section of the duct 9 and the magnetic field generating coils 14a to 14d are each rectangular in cross section. Because of the magnetic field characteristics of the magnetic field generating coils 14a to 14d, the inclination ∇B of the magnetic field increases toward the outer side of the cross section. Accordingly, the drift velocity having an obliquely downward direction increases, and hence, the divergence to a downward direction increases.
It is impossible to set the landing center of the ions of the cathode material 19 at the center of the surface of the substrate 6, for example. Even if the landing positions of the ions of the cathode material 19 are periodically shifted by periodically reversing the direction of the current flowing through each of the electromagnetic coils 14a and 14d, it is impossible to form a film on the substrate 6 by vapor depositing the cathode material 19 at a desired position on the substrate 6. In this respect, the vacuum arc vapor deposition apparatus is not satisfactory in obtaining a uniform film formation.